Voltage Collapse Proximity Indicator Research Articles

Impact of Wind Farm Location on Voltage Stability

Recently, the use of wind farm in power systems is increasing rapidly it is having a more noticeable impact on the manner in which these power systems operate. When large wind farms are connected to a power system network, voltage stability is a concern as it affects system operation. This paper investigates the impact of wind farm location on voltage stability in power system network when the reactive power limitation of wind generators is taken into consideration and a system reaches its maximum loading. An IEEE-14 bus test system was modified by connecting wind farms to the system at different buses, with different connection scenarios at different wind penetration levels, and the wind farm consists of several variable speed doubly fed induction generator (DFIG) wind turbines. In addition, a voltage collapse proximity indicator (VCPI), based on network loadability, is employed to investigate the contribution of wind generator location to voltage stability. The results of this paper show that system voltage stability is affected positively or negatively depending on the location of wind farm.

Voltage Constrained Reactive Power Planning Problem for Reactive Loading Variation Using Hybrid Harris Hawk Particle Swarm Optimizer

This study proposes the application of an efficient and hybrid meta-heuristic algorithm of Harris Hawk-Particle Swarm Optimizer (HHOPSO) for solving voltage constrained reactive power planning (VCRPP) problem. The prime objective of present work is diminishing the transmission loss and overall operating cost coupled with retention of voltage consistency and enhanced congestion management in transmission lines. The efficacy of the proposed algorithm is tested on standard IEEE 57 bus test system with optimal transformer tap settings, reactive generation control, generator voltage control and optimal control of Var sources. The best location of Var sources is determined by Voltage Collapse Proximity Indicator (VCPI) method. Simulation results are generated under normal and variable reactive power loading condition which makes the reactive power planning problem more challenging and validates the robustness of the proposed algorithm. The results of proposed algorithm when compared with the other optimization algorithms surfaced in contemporary state of art literature yields superior solution in maintaining diversity and solution optimality.

Weak bus-constrained PMU placement for complete observability of a connected power network considering voltage stability indices

Phasor measurement units (PMUs) are preferred for installation at weak buses in a power network. Therefore, the weak buses need to be located and the strategic locations of PMUs identified to ensure network observability. Thus, the primary aim of this work is to identify the placements of the maximum number of PMUs installed at the weak buses in the electrical network. The voltage collapse proximity indicator, line stability index, fast voltage stability index, and a new voltage stability indicator utilizing load flow measurement are used to determine the weak buses. A novel deterministic methodology based on a binary-integer linear programming model is then proposed to determine the optimal locations of PMUs. The effect of a single PMU outage considering the weak buses is also demonstrated. The effectiveness of the developed approach is tested and validated on the standard IEEE 14-, 118-, 300-, and New England 39-bus systems. The obtained results are also compared to those using different weak bus methodologies.

An optimal voltage stability enhancement in the power systems by locating optimal place with more contingency risk

The electrical components of a power system network take advantage to supply, transmission and service electrical power. Abnormal flow of voltage through the transmission lines might lead to big causes. Thyristor controlled series compensator (TCSC) devices are most frequently used device in the power to maintain the voltage stability. However, this device is costlier and cannot be fixed on every transmission line which would lead to more processing cost. Thus, the maintaining voltage stability of transmission lines with reduced production cost attracts a various researcher to find the novel approaches. In the existing system, to improve the stability of power system and minimize the losses by include the reactive power through TCSC device at applicable location by the algorithm of particle swarm optimization is available with the help of line stability index value. The PSO is constrained to poor exploitation problem which might generate inaccurate results. In the proposed research work, Biogeography Based Krill Herd (BBKH) method is used for optimal identification of TCSC's, STATCOM and UPFC size and location. Voltage collapse proximity indicator (VCPI) value is used in this work for the finding of the voltage instability measurement by finding the critical lines among the entire transmission lines. The proposed research effort is implemented in IEEE 39 test bus system using MATLAB software and verified, it furnishes improved outcome than other investigation methodologies.

An Optimal Voltage Stability Enhancement in the Power Systems by Locating Optimal Place with More Contingency Risk

The electrical components of a power system network take advantage to supply, transmission and service electrical power. Abnormal flow of voltage through the transmission lines might lead to big causes. Thyristor controlled series compensator (TCSC) devices are most frequently used device in the power to maintain the voltage stability. However, this device is costlier and cannot be fixed on every transmission line which would lead to more processing cost. Thus, the maintaining voltage stability of transmission lines with reduced production cost attracts a various researcher to find the novel approaches. In the existing system, to improve the stability of power system and minimize the losses by include the reactive power through TCSC device at applicable location by the algorithm of particle swarm optimization is available with the help of line stability index value. The PSO is constrained to poor exploitation problem which might generate inaccurate results. In the proposed research work, Biogeography Based Krill Herd (BBKH) method is used for optimal identification of TCSC's, STATCOM and UPFC size and location. Voltage collapse proximity indicator (VCPI) value is used in this work for the finding of the voltage instability measurement by finding the critical lines among the entire transmission lines. The proposed research effort is implemented in IEEE 39 test bus system using MATLAB software and verified, it furnishes improved outcome than other investigation methodologies.

Rolling horizon based multi‐objective robust voltage/VAR regulation with conservation voltage reduction in high PV‐penetrated distribution networks

Voltage/VAR regulation (VVR) implemented by capacitor banks (CBs), on-load tap changers (OLTCs), and photovoltaic (PV)-associated inverters is effective to enhance voltage stability and reduce power loss. On the other hand, conservation voltage reduction (CVR) has been widely adopted in distribution networks to reduce load demand. Existing works mainly focus on each of them. This paper proposes a VVR method with CVR, forming a multi-objective optimisation problem which minimises (i) voltage collapse proximity indicator (VCPI), (ii) load demand, and (iii) power loss. Besides, PV power generation as uncertainty significantly impairs the VVR results. To deal with the uncertainty issue, this paper proposes a rolling-horizon framework to determine VVR and applies Taguchi's orthogonal array testing (TOAT) to model the uncertain PV power generation, achieving rolling-horizon-based multi-objective robust VVR. The proposed model is tested and demonstrated on the IEEE 33-bus and 69-bus systems, and simulation results verify that the proposed method can support robust solutions of the multi-objective VVR problem for decision-making.

A comparison of the effectiveness of voltage stability indices in an optimal power flow

Voltage stability is very important, as without it voltage collapse will occur. There is therefore a need to incorporate the consideration of voltage stability into the optimal power flow (OPF). This paper presents a comparison of the effectiveness of five voltage stability indices (VSIs) when incorporated in an OPF. The improved particle swarm optimization (IPSO) algorithm is used to solve the OPF problem. The five VSIs investigated are the L‐index, fast voltage stability index (FVSI), line stability index (Lmn), online voltage stability index (LVSI), and voltage collapse proximity indicator (VCPI). The effectiveness of each VSI is considered in the terms of the generation cost, emission, transmission loss, and voltage stability. The IEEE standard 14‐, 30‐, 57‐, and 118‐bus test systems are used for the comparison. It is found that considering each voltage stability index as part of the objective function for the OPF provided different values of generation cost, emission, transmission loss, and maximum loadability. The results suggest that FVSI and Lmn provide the minimum generation cost values for all test systems, while VCPI and LVSI provide lower emission values for most systems. VCPI gives the lowest transmission losses for all systems, and the L‐index provides the maximum loadability for most systems. Incorporation of these indices into the OPF can provide the optimal values in different terms, and the most suitable voltage stability index will depend on the situation and size of the system, which needs to be judiciously chosen. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

Voltage Collapse Proximity Indicator based Placement and Sizing of Static VAR Compensator using BAT Algorithm to Improve Power System Performance

Power systems are becoming increasingly more complex due to the interconnection of regional system and deregulation of the overall electricity market. At present owing to the increase in power demand, power system has become more complex and heavily loaded, and is subjected to unstable or insecure operations. For secure operation, it is required to enhance the level of a security margin of the power system. In this paper sensitivity analysis based Voltage collapse proximity Indicator (VCPI) is proposed to select the optimal location of Static VAR Compensator (SVC). An Optimal Power Flow using BAT algorithm is carried out in order to find the optimal size of SVC which minimizes the total real power generation cost. Power System security is assessed using Line security index and voltage security index for IEEE 14 and IEEE 30-bus system using MATLAB Simulation. The results are presented and analyzed for BAT Algorithm based Optimal Power Flow without and with SVC and compared with Genetic Algorithm (GA).

Preventive control approach for voltage stability improvement using voltage stability constrained optimal power flow based on static line voltage stability indices

Voltage stability improvement is a challenging issue in planning and security assessment of power systems. As modern systems are being operated under heavily stressed conditions with reduced stability margins, incorporation of voltage stability criteria in the operation of power systems began receiving great attention. This study presents a novel voltage stability constrained optimal power flow (VSC-OPF) approach based on static line voltage stability indices to simultaneously improve voltage stability and minimise power system losses under stressed and contingency conditions. The proposed methodology uses a voltage collapse proximity indicator (VCPI) to provide important information about the proximity of the system to voltage instability. The VCPI index is incorporated into the optimal power flow (OPF) formulation in two ways; first it can be added as a new voltage stability constraint in the OPF constraints, or used as a voltage stability objective function. The proposed approach has been evaluated on the standard IEEE 30-bus and 57-bus test systems under different cases and compared with two well proved VSC-OPF approaches based on the bus voltage indicator L - index and the minimum singular value. The simulation results are promising and demonstrate the effectiveness of the proposed VSC-OPF based on the line voltage stability index.

Electric Power System Under-Voltage Load Shedding Protection Can Become a Trap

Problem statement: Under-Voltage Load Shedding (UVLS) protection of Electric Power Systems (EPS) is frequently used against Voltage Collapse (VC), however when there is automatic bus voltage regulation with excessive capacitive compensation, the UVLS scheme may not trip. In this case, load shedding must be based in a Voltage Collapse Proximity Indicator (VCPI). Many UVLS procedures may not be appropriate today. Approach: In order to elucidate the problem stated, several studies were carried out using MatLab/SimPowerSystems. In the first case, it was simulated a reduced electric system consisting of an infinite-bus feeding a load through a large impedance line. Two other cases were simulated now including a fixed capacitive impedance (representing a saturated SVC or similar) with 25 and 60 MVAr, both with a generator regulating the load bus voltage. Graphic curves representing the load bus voltage versus time were obtained with the application of a ramp power load. Results: In all cases the curves showed if there was sufficient time to command the UVLS scheme. The usual UVLS criteria failed for the third case. As the capacitive reactive power of the saturated compensation devices was increased, their equivalent capacitance, corresponding to the sum of maximum MVAr capacities, grows. The load demand increase, after MVAr saturation, can cause a voltage decrement which is too fast for UVLS adequate operation. Conclusion/Recommendations: Based in past experiences, any operator could be confident on existing UVLS protection of some area, but a VC can occur with the current situation without UVLS trip, as stated. It was suggested to check the current UVLS operation conditions, especially in areas where there was a growth of both load demand and reactive power resources. When UVLS method is found ineffective, then a suggestion is to replace it by a technique based upon some VCPI.

Differential evolution approach for optimal reactive power dispatch

Differential evolution based optimal reactive power dispatch for real power loss minimization in power system is presented in this paper. The proposed methodology determines control variable settings such as generator terminal voltages, tap positions and the number of shunts to be switched, for real power loss minimization in the transmission system. The problem is formulated as a mixed integer nonlinear optimization problem. A generic penalty function method, which does not require any penalty coefficient, is employed for constraint handling. The formulation also checks for the feasibility of the optimal control variable setting from a voltage security point of view by using a voltage collapse proximity indicator. The algorithm is tested on standard IEEE 14, IEEE 30, and IEEE 118-Bus test systems. To show the effectiveness of proposed method the results are compared with Particle Swarm Optimization and a conventional optimization technique – Sequential Quadratic Programming.

A NEW VOLTAGE COLLAPSE PROXIMITY INDICATOR

Voltage stability problems have been one of the major concerns for electric utilities as a result of increase demanding of electric power. This paper develops a new voltage collapse proximity indicator using catastrophe theory together with comparative singularity of power flow Jacobian and modal analysis. The application of the proposed indicator has been demonstrated on multimachine power systems

Estimating the voltage collapse proximity indicator using artificial neural network

Modern power systems are currently operating under heavily loaded conditions due to various economic, environmental and regulatory changes. Consequently, maintaining voltage stability has become a growing concern for electric power utilities. With increased loading and exploitation of the power transmission system, the problem of voltage stability and voltage collapse attracts more and more attention. A voltage collapse can take place in systems and subsystems and can appear quite abruptly. There are different methods used to study the voltage collapse phenomenon, such as the Jacobian method, the voltage instability proximity index and the voltage collapse proximity indicator method. This paper is concerned with the problem of voltage stability and investigates a proposed voltage collapse proximity indicator applicable to the load points of a power system. Voltage instability is early predicted using artificial neural networks (ANN) on the basis of a voltage collapse proximity indicator. Different system loading strategies are studied and evaluated. Test results on a sample power system demonstrate the merits of the proposed approach. The objective of this paper is to present the application of ANN in estimating the voltage collapse proximity indicator of a power system.

Power system security and voltage collapse: a line outage based indicator for prediction

With the increased loading and exploitation of the power transmission system, the problem of voltage stability and voltage collapse is attracting more and more attention. Continuous monitoring of the system status is therefore a necessary requirement. This article is concerned with power system security and investigates a proposed voltage collapse proximity indicator. For each line of the system, a line stability index is calculated based on the power flow through that line. The value of the line stability index is then used for predicting contingency outage of the lines and hence study the voltage collapse of the system. The described technique does not involve computational complexities and therefore can be easily implemented. The performance of the proposed indicator was tested on the IEEE 24 bus Reliability Test System and was found to be accurate and computationally feasible.

Steady state voltage instability assessment in a power system

With the increase of loading and exploitation of power transmission system and also due to the improved optimized operation, the problem of voltage stability and voltage collapse attracts more and more attention. The phenomenon of possible steady state voltage instability is creating serious concern among operators of large interconnected power systems. Maintaining adequate system voltage has become a major problem, as utilities are being forced to operate the system close to the thermal capability or steady state voltage stability limit. A voltage collapse can take place in power systems or subsystems quite abruptly, which requires improved continuous monitoring of the system state. There are different methods used to study the voltage collapse phenomenon, such as the Jacobian method, the simplified Jacobian method, the multiple load flow method and the voltage collapse proximity indicator method. It is proposed to modify the method of multiple load flow to obtain the weakest buses and the maximum injected powers for each bus. The method of voltage collapse proximity indicators is also simplified. These different methods are applied on a simple power system to study the problem of voltage collapse, and a comparison is made between them with indicating the merits and demerits of each.

Weak bus-oriented optimal multi-objective VAr planning

This paper presents a weak bus-oriented criterion to determine the candidate buses for installing new VAr sources in the VAr planning problem. First, an efficient method, using a voltage collapse proximity indicator, is described for identifying weak buses. Then appropriate VAr planning in those weak buses can enhance the system security margin, in particular, to prevent voltage collapse. Next, the goal attainment (GA) method based on the simulated annealing (SA) approach is applied to solving general multi-objective VAr planning problems by assuming that the decisionmaker (DM) has goals for each of the objective functions. The presented method can both obtain a better final solution and reduce the solution space. Results of application of the proposed method to the AEP-14 bus system as well as to a large, actual-size system are also presented.

Efficient methods for identifying weak nodes in electrical power networks

The paper presents two computationally efficient and simple methods of identifying weak buses in electrical power systems. The main purpose of identifying weak buses is to maintain control of voltages at these buses, in particular to prevent voltage collapse. The first method is based on the right singular vector, corresponding to a minimum singular value of the power-flow Jacobian matrix, which indicates sensitive voltages. The second method is based on the voltage collapse proximity indicator. The presented methods are successfully applied to several systems.

Dynamical analysis of voltage collapse in longitudinal systems

In this paper an analysis of the voltage collapse phenomenon in longitudinal systems is presented. The analysis is performed through a small signal perturbation approach where the nonlinear multimachine dynamic model is linearized around a steady-state operating point, and the stability of the system is evaluated through the eigenvalues of the Jacobian matrix of the dynamic state equations. The analysis clarifies the difference between the maximum loadability point and the voltage stability limit. In addition, a voltage collapse proximity indicator, taking into account the dynamic of the system, is proposed and tested in three different networks.

Study of voltage collapse at converter bus in asynchronous MTDC-AC systems

This paper presents the analysis and study of voltage collapse at any converter bus in an AC system interconnected by multiterminal DC (MTDC) links. The analysis is based on the use of the voltage sensitivity factor (VSF) as a voltage collapse proximity indicator (VCPI). In this paper the VSF is defined as a matrix which is applicable to MTDC systems. The VSF matrix is derived from the basic steady state equations of the converter, control, DC and AC networks. The structure of the matrix enables the derivation of some of the basic properties which are generally applicable. A detailed case study of a four-terminal MTDC system is presented to illustrate the effects of control strategies at the voltage setting terminal (VST) and other terminals. The controls considered are either constant angle, DC voltage, AC voltage, reactive current and reactive power at the VST and constant power or current at the other terminals. The effect of the strength of the AC system (measured by short circuit ratio) on the VSF is investigated. Several interesting and new results are presented. An analytical expression for the self VSF at VST is also derived for some specific cases which help to explain the number of transitions in VSF around the critical values of SCR.